Dwindling conventional fossil resources are amongst the greatest global challenges currently being faced, and this has rightly spurred ever increasing research efforts into new utilizations of renewable energy resources. The intermittent nature of most renewable energy sources (e.g. solar and wind) entails a need for energy storage. Energy can be stored safely and conveniently as chemical bonds. Methane reduced from CO2 is one such possible energy carrier. This energy carrier could then be introduced in a closed loop cycle, with recovery of the spent carrier (CO2) from the atmosphere making the technology carbon neutral—provided a renewable energy source such as sunlight or wind is used to drive the process. Furthermore, the recent utilization of fossil natural gas resources in the US has spurred a large investment in industries relying on cheap natural gas. Renewable methane production from CO2 reduction would support this industry beyond the lifetime of the current fossil resources and thus gradually increase the market for these new technologies.
Electrochemical CO2 reduction (Direct CO2 Reduction Reaction, DCRR) has been realized to alcohols on noble metals, and to alkanes on Cu. These technologies are still severely limited from making a significant impact by at least the following: significant H2 production (by-product) as well as high cost for the noble metals and low selectivity for a single alkane/alkene product for Cu. Of further complication, a small 110 mV thermodynamic difference separates CO2 reduction to CO (a key intermediate) vs. proton reduction to H2. This class of catalysts performs this reaction at lower potentials, i.e. higher efficiencies than any previous flat pure metal electrodes. While it might seem reasonable to propose to use the worst H2 evolution catalysts available (e.g., SnO2), reduction of CO to valuable hydrogenated products requires a catalyst that is capable of showing some measure of activity towards the reduction of protons (hydrogen cations). Understanding and controlling this apparent paradox is key to achieving selective DCRR catalysts.
Thus, improved and more efficient DCRR catalysts are eagerly sought.